In the health care field, syringes have different functions. The primary function is to introduce and/or withdraw fluids into and from the body. The introduction of fluids into the body typically requires precise metering and the syringes are relatively expensive because of the close tolerances required between the plunger of the syringe and the sleeve within which it reciprocates. The withdrawal of fluids from the body may not require precise metering but usually the same, relatively expensive, syringe will be used simply as a matter of convenience.
Another function of syringes is the flushing of catheters and the like which catheters are in situ. An anti-coagulant, such as herapin, flushes the catheter which is subsequently aspirated to ensure that the catheter is still functioning properly. Syringes used for this purpose do not need to precisely meter the fluid into the body and therefore, the close tolerances required of those syringes specifically used for introducing a fluid into the body are not required.
The present invention relates to a syringe which, in effect, is plungerless and which can deliver predetermined amounts of fluid, such as an anti-coagulant, into a catheter or the like instrument.
Broadly the invention comprises a sealed syringe having a collapsible body. The syringe comprises a dispensing tip and an actuating tab. The syringe is formed, filled with a metered amount of fluid and sealed. The collapsible body is characterized by a plurality of steps or ribs which engage one another when the body is collapsed. The steps allow the body to be collapsed in an index or calibrated manner.
In a preferred embodiment, the collapsible body is bell-shaped and the steps comprise a plurality of concentrically arrayed ribs formed in seriatim on the outer surface of the body. The ribs define walls or membrane sections therebetween. When the body is collapsed, one rib is telescopically received and secured within the next succeeding rib. The telescoped ribs ensure the body stays in its collapsed position. If fluids are to be aspirated from the body, the dispensing tip remains in situ and the actuating tab is withdrawn and the ribs are released from one another. The movement of one rib within another is smooth, not unlike a piston sliding into a cylinder. This ensures a constant even pressure in dispensing the fluid. It prevents surges and the creation of backpressure which would cause uneven flow.